This invention relates to a moving picture coding method for coding a moving picture, a moving picture decoding method for decoding a coded moving picture, and apparatuses therefor.
In the case of digitizing a signal of a moving picture to record and transmit digital data thus obtained, its data quantity becomes extremely large. For this reason, coding (compression) is implemented to that data. As a representative coding system, there is so called MPEG (Moving Picture Expert Group) system. This MPEG is general name of the moving picture coding system which has progressed in WG (Working Group) 11 of SC (Sub Committee) 29 of JTC (Joint Technical Committee) 1 of ISO (International Standardization Organization) and IEC (International Electrotechnical Commission).
Moreover, as a widely known format in the case of handling a picture signal by a digital signal, there is Recommendation 601 (Rec. 601) of so called CCIR (Comite Consultatif Internationale des Radio-communications (International Radio Consultative Committee)). This Rec. 601 is the worldwide standardized format of digital picture based on the component (so called 4:2:2 component) coding system.
In the MPEG, the above-mentioend Rec. 601 format is used as input/output picture format. In the NTSC zone of the scanning line 525 lines/30 Hz, an input/output picture format as shown in FIG. 11, for example, has been most popularly used. For example, in MPEG2 (MPEG phase-2), picture of picture frame of frame of 720 pixelsxc3x97480 lines of Rec. 601 format is handled. On the other hand, in MPEG1 (MPEG phase-1), picture of picture frame of frame (SIF) of 360 pixelsxc3x97240 lines obtained by thinning pixels so that resolutions in the longitudinal and lateral directions are respectively equal to one half thereof is handled.
A technique to allow the transmission format of picture to have a relationship such that the ratio between length and breadth of picture frame is expressed as 1:2 in dependency upon difference of resolution is convenient in a hierarchical manner. This is related to the following two reasons.
First reason is that hardware configuration of thinning filter and/or interpolating filter having ratio of 1:2 are simpler than those of filters having other ratios.
Second reason is that, in the case of constituting picture coding/decoding apparatuses, it is possible to process picture data by four image LSIs disposed in parallel for picture having resolution which is one half of picture to be processed.
An example of filter coefficients of the thinning filter is shown in FIG. 12.
Moreover, since there is employed a scheme to handle picture in a manner divided into small blocks called macro blocks of 16 pixelsxc3x9716 lines, it is preferable that the horizontal and vertical sizes of picture are multiple of 16 when coding efficiency is taken into consideration. From a viewpoint of this, picture frame size of 720 (=16xc3x9745) pixelsxc3x97480 (16xc3x9730) lines is preferable size. For reasons described above, in the NTSC zone, picture of picture frame of frame of 720 pixelsxc3x97480 lines of Rec. 601 format has been widely handled.
On the other hand, CCIR recommended broadcasting stations (television stations) that picture signals of 483 lines or more (about 483xcx9c486 lines) must be transmitted in the standard television broadcasting in the NTSC zone. At this time, if picture coding is carried out by MPEG as in the prior art, it is required to increase the number of macro blocks by one column in a longitudinal direction to carry out processing of 720 pixelsxc3x97496 (480+16) lines. This results in requirement of increase in the coding processing ability of about 3.5% as compared to the case where frame of 720 pixelsxc3x97480 lines is handled.
This is inconvenient for a system only having a decoding apparatus which can merely handle so far as picture of picture frame of frame of 720 pixelsxc3x97480 lines. For example, when the recording system of the digital video disc and the broadcasting system of the digital television are the same MPEG, it is considered that there results the merit that it is sufficient to have only either one of decoding apparatuses. However, in the case where decoding apparatus of video disc player has only processing ability of picture frame of 720 pixelsxc3x97480 lines, it is unable to receive picture signals in digital television broadcasting by that decoding apparatus. This gives rises to extremely waste from a viewpoint of effective utilization of hardware resource.
Meanwhile, CCIR only recommended that picture signals of 483 lines or more (about 483xcx9c486 lines) in the standard television broadcasting in the NTSC zone must be transmitted, but whether or not the receiving side decodes picture information of 480 lines or more is arbitrary. For this reason, in the case where, the receiving side is a decoding apparatus having only processing ability of picture frame of 720 pixelsxc3x97480 lines, if it is possible to decode only such picture frame, this is very desirable.
To meet the above-described requirement, it becomes necessary to realize a moving picture coding technology required for providing moving picture coded information (broadcasting) having flexibility and a decoding method there for such that in the case where the receiving side is a decoding apparatus having processing ability of picture frame of 483 lines or more, received all picture signals can be reproduced, while in the case where the receiving side is a decoding apparatus having only processing ability of picture frame of 480 lines, only the decordable picture portion can be reproduced.
To realize this, it is necessary to solve problems described below.
First, such a task must be accomplished to permit discrimination as to whether or not only picture information of reproducible picture frame is taken out from received coded information.
Secondly, since in the coding method using motion compensating prediction between pictures such as MPEG, etc., pictures have correlation therebetween in a time base direction, in the case where reference is made to the outside (line portions indicated by 16 lines in the figure, for example) of the reproducible picture frame by motion compensation as shown in FIG. 13, motion compensation is unable to be carried out. As a result, decoding cannot be made. Accordingly, it is necessary to take any measure for this problem.
Namely, the case where coded information of 496 lines is received by decoder only having processing ability of picture frame of 480 lines is taken as an example in FIG. 13. In the case of the example of FIG. 13, motion compensation in directions indicated by arrows a, b in the figure from within the picture frame of 480 lines of past picture or future picture to current picture can be made, but motion compensation in directins indicated by arrows c, d in the figure from within the picture frame beyond 480 lines of past picture or future picture (line portions indicated as 16 lines in the figure) to current picture cannot be carried out.
In view of the above, in order to satisfy the above-mentioned requirements, an object of this invention is to provide a moving picture coding method required for providing moving picture coded information (broadcasting) having flexibility and a decoding method corresponding thereto such that in the case where the receiving side is a decoding apparatus having processing ability of picture frame of 483 lines or more, received all picture signals can be reproduced, while in the case where the recieving side is a decoding apparatus having only processing ability of picture frame of 480 lines, only the reducible picture portion can be reproduced.
This invention has been proposed in order to solve the above-described problems. A moving picture coding method of this invention comprises the steps of: dividing a picture signal of a picture frame of N pixelsxc3x97M lines (horizontal N pixels, vertical M lines) to be coded between a first picture portion serving as an internal picture portion having a picture frame of N1 pixelsxc3x97M1 lines (N1xe2x89xa6N, M1xe2x89xa6M) and a second picture portion serving as a picture portion outside the first picture portion; and dividing the first picture portion and the second picture portion in independent predetermined divisional units comprised of a plurality of pixels, whereby in transmitting coded information of the predetermined divisional units belonging to the second picture portion, peculiar discrimination codes are respectively added to headers of the divisional units.
In the above-mentioned moving picture coding method, at the time of motion compensating prediction, it is inhibited that the first picture portion of a current coded picture makes reference to the second picture portion of reference picture. Moreover, motion compensating prediction implemented to the second picture portion of current coded picture does not place restrictions on reference picture.
It should be noted that when size of unit block for carrying out motion compensating prediction is assumed to be N2 pixelsxc3x97M2 lines, setting is made such that N1 is multiple of N2 and M1 is multiple of M2. In addition, setting is made such that N1 and M1 are both multiple of 16.
Further, a moving picture decoding method of this invention is characterized in that when only decoding ability of the picture frame of N1 pixelsxc3x97M1 lines is provided, only the first picture portion is reproduced, and any one of peculiar discrimination codes added to headers of predetermined divisional units comprised of a plurality of pixels belonging to the second picture portion is detected with respect to the second picture portion to thereby discriminate the second picture portion, thus making it possible to read, in a skipped manner, coded information of the second picture portion.
Also in this decoding method, when size of unit block for carrying out motion compensation is assumed to be N2 pixelsxc3x97M2 lines, N1 is multiple of N2 and M1 is multiple of M2. In addition, N1 and M1 are both multiple of 16.
Meanwhile, for example, in the case where a frame picture signal to be transmitted is a picture signal of 483 lines or more required for the television broadcasting of the NTSC system, the first internal picture portion becomes 480 lines.
In this case, frame picture signal of 483 lines or more required for the television broadcasting of the NTSC system is divided between a first picture portion of 480 lines and a second picture portion serving as a picture portion of the highest portion or the lowest portion of the picture except for the first picture portion, whereby when only decoding ability of picture frame of 480 lines is provided, only the first picture portion is reproduced, and any one of peculiar discrimination codes added to headers of predetermined divisional units comprised of a plurality of pixels belonging to the second picture portion is detected with respect to the second picture portion to thereby discriminate the second picture portion thus to read, in a skipped manner, coded information of the second picture portion.
In accordance with this invention, in coding moving picture, picture signal of picture frame of N pixelsxc3x97M lines (horizontal N pixels, vertical M lines) to be coded is divided between first picture portion serving as the internal picture portion having picture frame of N1 pixelsxc3x97M1 lines (N1xe2x89xa6N, M1xe2x89xa6M) and second picture portion serving as picture portion outside the first picture portion to divide the first picture portion and the second picture portion in independent predetermined divisional units comprised of plural pixels, whereby in transmitting coded information of the predetermined divisional units belonging to the second picture portion, peculiar discrimination codes are respectively added to headers of predetermined divisional units.
Accordingly, in the case where only decoding ability of picture frame of N1 pixelsxc3x97M1 lines is provided when such a coded signal is decoded, only the first picture portion is reproduced, and corresponding peculiar discrimination code is detected with respect to the second picture portion to thereby discriminate the second picture portion, thus making it possible to read, in a skipped manner, coded information of that picture portion.